Tuesday, 6 December 2011

Chapter 8: The Water Cycle

Hydrologic Cycle
The water cycle is also called by hydrologic cycle. It is a conceptual model that describes the storage and movement of water between the biosphere, atmosphere, lithosphere and the hydrosphere. Water on this planet can be stored in ant one of the following reservoirs : atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields and ground water.
Water moves from one reservoir to another by processes such as evaporation, condensation, precipitation, sublimation, transpiration and melting.

Heat from the Sun changed the liquid surface water ( oceans, lakes, wetlands, rivers ) into water vapour, which rises into the air. This is called evaporation.


Green plants, especially trees, suck water out of the earth with their roots and pump it up throughout their bodies, ending in the leaves, which release water vapour. This is called transpiration. Large trees transpire hundreds of gallons of water a day.


Precipitation and sublimation
Above the ocean and rain forests, water vapour condenses into clouds. Wind moves the clouds of vapour. The cloud release their water in liquid phase ( rain ) or crystal phase ( snow ) when they get too heavy to hold themselves in the air. Rain and snow are the two types of precipitation. Rain is the main way in which water in the sky comes down to earth. In cold countries, the water droplets in the clouds turns directly to snow by sublimation. The water runs-off or soaks into the ground and eventually some of it flows into the ocean, where the circle repeats.


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